Compression bags 101, 201 having an article containing portion 102, 202 enveloped by flexible resin sheets as joined together by heat-sealing or the like at their predetermined spots have been widely used.
An opening 103, 203 through which the article M is inserted or removed from the article containing portions 102, 202 is provided in said compression bags 101, 201. Also, a closing means 104, 204 such as a fastener for keeping the openings 103, 203 closed is provided in the opening 103, 203.
Though various embodiments of such compression bags exist, roughly speaking, two types of compression bags 101, 201 described below exist.
First, it is disclosed by Japan Laid-open Patent Application No. 9-309544. Simply illustrated in FIG. 11, a compression bag 101 includes a check valve 105. A check valve 105 used in the compression bag 101 comprises an outer tubular portion 107 of a flexible resin sheet which is formed into a flat tube so as to connect a space of the article containing portion 102 with the outside of the compression bag 101, and a valve body sheet 106 made of a flexible resin sheet provided inside the outer tubular portion 107 as shown in FIG. 11(B).
Since said valve body sheet 106 functions to permit an air-flow F1 from the article containing portion 102 to the outside of the compression bag 101 and to block the reverse air-flow F2, an evacuated condition in the article containing portion 102 can be maintained by the check valve 105 after evacuation.
Having contained the article M in the article containing portion 102 and closed by the closing means 104, said compression bag 101 can maintain an evacuated condition after discharging the air in the article containing portion 102 through the check valve 105.
This structure is particularly effective for a voluminous article M like clothing and blanket, and the air in the article M can be discharged outside the compression bag 101, which can make compact while containing the article M. Thus, the compression bag 101 is suitable for a preservation bag for clothes or a bag used during travel.
The check valve 105, however, is manufactured separate from the bag sheets 102a, 102b constituting the article containing portion 102, and is incorporated into the article containing portion 102 later when the article containing portion 102 is formed afterward, whereby each production step of manufacturing the check valve 105 and incorporating it into the article containing portion 102 is required. This may complicate the production steps for the compression bag 101, and a special production system must be employed for this purpose, thus resulting in increase of the production costs.
Also, when the check valve 105 is incorporated in the compression bag 101 as described above, heat-seal 108 is provided as shown in FIG. 11(B), and the bag sheets 102a, 102b constituting the article containing portion 102 and the outer tubular portion 107 of the check valve 105 are bonded. Said heat-seal 108 is formed on the bag sheets 102a, 102b where the check valve 105 slips therebetween by pressing of a heated mold from outside the bag sheets 102a, 102b in a manner of crossing the check valve 105.
Accordingly, in order not to bond the outer tubular portion 107 of the check valve 105 and the valve body sheet 106 together against heat-sealing, a coating material 106b, for example, for preventing the face 106a from melting by heat during the heat-sealing is applied to the face 106a of the valve body sheet 106 opposite to the inner face of the outer tubular portion 107. But, even though the coating material 106b is applied, the inner side of the outer tubular portion 107 where the coating material 106b is not applied may melt under thermal influence of the heat-sealing, resulting in a slightly heat-sealed condition (a slight heat-seal 109) between the outer tubular portion 107 and the valve body sheet 106. Although the slight heat-seal 109 is actually not so strong against an external force, the internal pressure of the article containing portion 102 may increase in the initial use of the compression bag 101, from separation of the outer tubular portion 107 and the valve body sheet 106 caused by detachment of the slight heat-seal 109 till opening of the check valve 105, entailing resistance in evacuation, requiring much time to complete the evacuation. In a certain case, the drawback leads to a risk of burst of the bag sheets 102a, 102b of the article containing portion 102. Such a disadvantage is particular in a manual evacuation of the article containing portion 102.
Another embodiment of the compression bag 201 is disclosed by U.S. Pat. No. 6,116,781, as shown in FIG. 12. In this particular compression bag 201, an intermediate sheet 206 is disposed between the two opposite bag sheets 202a, 202b so as to make an air passage therebetween, forming a check valve 205. Said check valve 205 can achieve a non-return function by a tight contact of the bag sheets 202a, 202b and the intermediate sheet 206.
Unlike the above-described compression bag 101, since a check valve 205 in the compression bag 201 is integrally formed from the beginning, it is an advantage that only one single production step is required in the production process. Additionally, a problem of forming a slight heat-seal 109 taking place when a separate check valve 105 as described above is incorporated will not occur.
The intermediate sheet 206 in this compression bag 201, however, is simply disposed between the bag sheets 202a, 202b, the arrangement of which does not achieve a complete non-return function, whereby it is impossible to maintain a secure evacuation of the article containing portion 202.
In view of these problems, the object of the present invention is to provide a production method for a compression bag and the compression bag, wherein the compression bag may be produced in a single production step which leads to reducing production costs, being able to maintain a secure evacuation of the article containing portion and easily evacuate against low pressure resistance even in a manual evacuation.